Conventional spray booms are well known. Spray booms are employed on fixed wing aircrafts, helicopters and ground rigs.
Conventional spray booms used on fixed wing aircraft operate on the principle of high pressure/low volume output. Essentially the suspensions or solutions to be sprayed onto pastures or ground from a conventional fixed wing spray boom are physically forced under pressure through outlets or nozzles along the spray boom. A conventional fixed wing spray boom is unable to spray thick suspensions of lime, fertilisers, seeds, biological agents or pelletized products, as it is not possible under the high pressure/low volume principle of operation to force out thick suspensions. A similar problem is encountered when a solution is particularly viscous.
Another problem associated with conventional fixed wing spray booms is that the outlets or nozzles along the spray boom have a tendency to block. Such blocking normally occurs when the pilot stops dispensing the suspension or solution from the spray boom and turns the aircraft, to make another pass of the pasture or ground. When the pilot starts respraying often the nozzles have become blocked with a residue of the suspension or solution being dispensed. It is not possible to clear the nozzles of such conventional spray booms, unless the pilot returns to ground and manually unblocks the nozzles.
The conventional spray booms employed with fixed wing aircraft operate using a sprayer having a high pressure/low volume nozzle. The flow of a solution to be dispensed can be stopped by controlling the flow of the solution to the boom. On each nozzle a pre-loaded diaphragm sensitive to pressure is employed to actuate a small valve within the nozzle itself. When the pilot cuts the flow of solution to the boom, the diaphragms and valves within the nozzles act to cause an immediate stop to the flow of liquid from the nozzles, preventing any low pressure dripping from liquid remaining in the boom and the piping from the boom to the pump. This system is unsuitable for dispensing suspensions as the mechanisms within the nozzles become clogged and the nozzle mechanisms can not be reactivated to enable the suspension to flow when the pump is applied.
Ground rig sprayers are also unable to spray thick suspension on to pasture using existing boom and nozzle design as they are subject to the same blockage factors as seen on conventional airborne spray booms. One method of overcoming this problem is to utilise large volumes of water to dilute the suspension. However, such a method is relatively expensive. Additionally, the forward speed of a ground rig sprayer does not provide a sufficient wind shear across a spray boom to atomise suspensions.
Helicopters have also been employed for spraying suspension. It has been shown that the droplet size and coverage from a helicopter is less adequate than that obtained when spraying from a conventional fixed wing aircraft. The lower airspeed of helicopters is disadvantageous when spraying, especially when using large orifice sizes to dispense product at a rate greater than 100 kg to the hectare.
In recent years, many countries have introduced legislation that provides guidelines and regulations that local bodies should adhere to in the formulation of their individual air, land and water plans. In New Zealand for example, the Resource Management Act 1991 specifies that, for fertilisers and the like, application rates above those recommended are to be classed as contaminants. Such provisions have led to a need for aerial applicators to improve their spread and accuracy of placement of materials to be applied to pasture or crops. Furthermore, conventional spraying methods for the application of dry agricultural lime do not comply with the dust emission requirements of New Zealand's Resource Management Act.
It is an object of the present invention to overcome some of the difficulties and disadvantages of conventional spraying or top dressing means, particularly for fixed wing aircraft, or to at least provide the public with a useful choice.